This invention relates to a wound-tape radius detection system for detecting the radius of a tape wound on a reel in a reel to reel tape recorder such as an audio tape recorder, a video tape recorder, or a data tape recorder. The wound-tape radius detection system may be applied to, for example, a tape-end detector.
In a tape recorder, a tape is transported from one reel (e.g., a supply reel) to the other reel (e.g., a take-up reel) in for example, recording, playback, and fast forward modes and vice versa in a rewind mode. As the tape is being transported, radii of the tapes wound on the reels are inversely with respect to each other.
In the case where the tape is expected to be smoothly stopped in a small period of time from the fast forward or fast rewind mode, a greater braking torque must be applied to the reel having the larger radius of wound tape, and a smaller braking torque should be applied to the other reel with the smaller radius of tape. Further, in the case where the tape is started to begin transport from the stop mode, the reels must be controlled in response to the wound-tape radii. Because wound-tape radius detection systems of the prior art require a complicated construction, they have not been applied to a tape recorder.
Furthermore, it is often desirable not to completely wind or rewind the tape on the take-up or supply reel in order to avoid re-threading of the tape. For this purpose, there has been proposed a tape end detector, as disclosed in the U.S. Pat. No. 4,213,583 entitled "REEL DRIVE MOTOR CONTROL SYSTEM FOR CASSETE/CARTRIDGE TAPE RECORDERS" issued to Mitani et al. and assigned to the present assignee, in which the tape end is detected through the calculation of the ratio between the rotational speeds of the take-up and supply reels. The tape-end detection is based on the fact that the length of the tape encased in a cassette or a cartridge is prefixed and that the rotational speed of the supply or take-up reel is in direct proportion to the length of the tape actually wound on the reel, whereby the location of the front or rear end of the tape can be predicted through the calculation of the above-mentioned speed ratio. However, this tape-end detection is not applicable to an open-reel type tape recorder.